Magnetostrictive actuators are generally known in the art, wherein one end of the active element is fixed or grounded while the other end undergoes a limited stroke of mechanical motion. Heretofore, one standard type of such actuator also included a prestress mechanism to bias the active element made of Terfenol, Terzinol or some other magnetostriction material and a ferromagnetic casing providing a return path for magnetic field energy produced during energized operation of the actuator.
It is also known in the art, as reflected by the disclosure of a linear magnetostrictive motor in U.S. Pat. No. 5,039,894 to Teter et al., that greater magnetostriction occurs in a single crystal material element along its crystalline axis. Accordingly, the prestress and magnetic circuit applied was arranged to obtain output motion in a crystallographic direction of growth of the magnetostriction material along its crystalline axis, as the usual direction of usage associated with a relatively short stroke of 0.001 dl/l for example. It is therefore an important object of the present invention to provide a compact magnetostrictive type of linear motion actuator having a substantially longer output stroke so as to extend its usefulness in many applications.
In accordance with the present invention, a linear motion actuator includes a magnetic circuit assembly of layers through which a substantially longer output stroke is achieved in a direction perpendicular to the crystallographic direction of deformation imposed by magnetic fields applied to the magnetostriction material. According to one embodiment, slabs of said magnetostriction material are positioned on opposite sides of interconnectors respectively associated with the layers of the circuit assembly to which magnetic fields are applied by wiring coils to which electrical energy current is supplied. During each operational cycle, magnetostrictively produced deformation forces produced by the applied magnetic fields are transferred in sequence in a direction perpendicular to the crystalline axis of the magnetostriction slabs from a lowermost layer at the actuator ground end to the uppermost layer from which the output motion is obtained. Such layers of the magnetic circuit assembly are held assembled between a fixed ground and an uppermost output element of the actuator spaced therefrom along a bias axis under an adjustable prestress which accommodates lateral displacement of the output element relative to such bias axis.